Miniaturized camera systems are, for example, incorporated in handheld devices with imaging capability, such as barcode or text scanners, cameras, video recorders and electronic pens. Such camera systems generally include an imaging arrangement which defines an object plane and an image plane, whereby an object which is located within a field of view in the object plane is reproduced as an image in the image plane. The camera systems also include a radiation sensor which is essentially co-located with the image plane, to physically or electronically capture the image.
It may be important to precisely locate the image plane on the radiation sensor inter alia, to ascertain that the optical system produces an image of a well-defined part of the object plane. To this end, it may be necessary to keep both manufacturing and assembly tolerances of the optical system low. The absolute values of such tolerances may be very small in the case of compact imaging arrangements for handheld devices.
Assembly tolerances may be minimized by operatively engaging at least part of the imaging arrangement to the radiation sensor. For example, the imaging arrangement may include guiding surfaces that are designed to engage with corresponding surfaces on the radiation sensor to precisely locate the imaging arrangement with respect to the sensor, or vice versa. Applicant's international publication WO 03/001358 discloses an electronic pen with such an imaging arrangement. The camera system of the electronic pen is carried by a cylindrical stopper which is arranged in the front end of the pen. The imaging arrangement includes a tubular holder which contains optical components, such as one or more lenses, an aperture stop, a filter, etc. A pocket is formed at the rear end of the holder for form-fitted mounting of a two-dimensional radiation sensor, such as a CCD or CMOS sensor.
Such an optical system may require complex assembly steps in production, possibly involving manual labor. Further, the imaging arrangement has to be designed for a specific sensor geometry, resulting in a need for re-design whenever there is a change in the geometry of the sensor.